Which of the following is NOT one of the four inhibiting factors for Stay at Gate flights?

The correct choice is identified by recognizing that system efficiency is not categorized as one of the four inhibiting factors for Stay at Gate flights. The four factors typically include considerations directly related to the aircraft's operational capabilities and safety compliance priorities.

Payload optimized refers to how the aircraft is loaded to ensure it operates within its weight limits, which is a crucial consideration during boarding and deplaning processes. Balance critical highlights the importance of maintaining an even weight distribution throughout the aircraft to ensure safe flight operations. Dangerous goods compliance is a vital regulation ensuring that hazardous materials are handled and stowed correctly to prevent risks during the flight.

System efficiency, while important in the broader context of airline operations, does not specifically inhibit a Stay at Gate flight like the other factors mentioned. Thus, it stands apart as a concept related more to operational practices than to immediate safety and compliance factors affecting flight dispatch decisions.